Validate the height values entered into the layer height table.

Clamp these values between the minimum of min_layer_height per nozzle
and the maximum of max_layer_height per nozzle.
Don't allow entering zero layer height to trim an object,
the cut dialog should be used instead.

Fixes https://github.com/prusa3d/Slic3r/issues/235

lib/Slic3r/GUI/Plater.pm

@@ -1819,6 +1819,7 @@ sub object_settings_dialog {
     my $dlg = Slic3r::GUI::Plater::ObjectSettingsDialog->new($self,
 		object          => $self->{objects}[$obj_idx],
 		model_object    => $model_object,
+        config          => $self->GetFrame->config,
 	);
 	$self->pause_background_process;
 	$dlg->ShowModal;